Chlorites are a class of reagent chemicals which have many commercial uses and many processes for preparation have been used. More recently, the method of choice has been by the reaction of chlorine dioxide, a reducing agent and an alkaline solution. The following U.S. Letters Patent disclose variations of this process:
______________________________________ Inventor(s) U.S. Pat. No. ______________________________________ Vincent 2,092,945 Cunningham 2,194,194 Soule 2,332,180 Wagner 2,616,783 Hirschberg et al 3,101,248 Du Bellay et al 3,450,493 Callerame 3,828,097 Miller 4,087,515. ______________________________________
Vincent discloses preparation of water soluble chlorites by reacting chlorine dioxide with an alkaline solution which contains a reducing agent. PA1 Cunningham discloses preparation of chlorites by the reduction of chlorine dioxide with metallic reducing agents in the presence of an alkaline solution. PA1 Soule discloses preparation of chlorites by the addition of chlorine dioxide to a solution of hydrogen peroxide in an alkaline solution made alkaline with an alkali metal bicarbonate. PA1 Wagner discloses a process for preparing a solid chlorite by reacting chlorine dioxide in an alkaline solution containing a reducing agent, e.g. hydrogen peroxide. PA1 Hirschberg et al disclose a process for the manufacture of alkali metal chlorides using a mercury amalgam reducing agent in a pH range maintained between pH 7-9. PA1 Du Bellay et al disclose a process of producing alkali metal chlorites in which an alkaline solution of hydrogen peroxide reacts with chlorine dioxide which is bubbled therethrough to yield an alkali metal chlorite. Measurements of redox potential and pH are made, and the reactants are added to a reaction vessel based on the redox and pH measurements. PA1 Callerame discloses a process for preparation of chlorous acid that involves a reaction of a chlorate with a nitrite in a column containing a cation exchange resin. PA1 Miller discloses a process for the production of alkali metal chlorites that involves a reaction of chlorine dioxide with alkali metal amalgams under an atmosphere of nitrogen gas.
All of these above processes are conducted at atmospheric pressure or at a pressure greater than atmospheric pressure.
In those references which use chlorine dioxide, alkali and peroxide, the chlorine dioxide is added to the solution containing peroxide and alkali and the reaction takes place in solution.
One preferred commercial method of manufacturing sodium chlorite starts with the electrochemical formation of sodium chlorate. The sodium chlorate is reduced to form chlorine dioxide. Sodium hydroxide having a low iron content is dissolved in water and cooled to a temperature of approximately 40.degree. F. In the process, hydrogen peroxide is added to the sodium hydroxide solution while maintaining the temperature of the reagents to about 35.degree.-40.degree. F. The gaseous chlorine dioxide is then added to the solution of sodium hydroxide and hydrogen peroxide while maintaining a solution temperature of approximately 35.degree.-40.degree. F. The control of the temperature is critical because at room temperature and warmer, the peroxide decomposition in caustic is accelerated and the process rapidly loses efficiency. A disadvantage with this method is the size of the equipment required to produce the chlorite. A reaction in solution (liquid/liquid) involves large volumes to be commercially useful. The kinetics of a liquid/liquid reaction requires a finite time to permit the reaction to be initiated and to proceed to completion. Thus, the solutions must be held in large tanks or holding vessels. Typically, the equipment occupies a volume of approximately 10,000-15,000 cubic feet depending on the plant capacity. Also, the equipment is expensive to procure, install and maintain.
Thus, despite the wide-spread use of these chemicals and the efforts of numerous investigators over a period of years, the commercial production of chlorite is comparatively expensive, requiring large equipment, significant land area, maintenance, large volumes of in-process liquids, and special temperature conditions. A need exists to simplify the process and provide a more economical product.